The invention relates to electronically controlled capacitor discharge ignition systems, and more particularly, to an interlocking shut-off arrangement for such a C.D. ignition system. Still more particularly, the invention relates to such a C.D. ignition system utilized to control the operation of an internal combustion engine for driving the cutting blade of a lawn mower, and including an interlocking shut-off arrangement operative, for example, to require that the lawn mower grass bag and chute, or grass discharge cover, be in proper position in order to operate the engine. Attention is directed to the following U.S. patents which disclose electronically controlled C.D. ignition systems having a single ignition shut-off switch:
______________________________________ Anderson 3,960,128 issued June 1, 1976 Cavil 4,074,669 issued Feb. 21, 1978 Haubner 3,900,016 issued Aug. 19 1975 ______________________________________
Haubner discloses that electronically controlled C.D. ignition systems having shut-off or stopping switches are known wherein the control current to the ignition SCR is interrupted so that the SCR is no longer turned on, and hence, so that the capacitor cannot be discharged. Haubner notes that with such an arrangement, supplementary precautions must be taken to protect the ignition capacitor and SCR from excess voltage, and states that it is an object of his invention to provide a capacitor discharge ignition system with an engine stopping switch so arranged so that there is no overloading by excess voltages.
Attention is also directed to the following patents which disclose engine starting or engine operating interlocking switch arrangements for various types of lawn mowers:
______________________________________ Nofel 3,969,875 issued July 20, 1976 Uhlinger 4,043,102 issued Aug. 23, 1977 Thorud 3,750,378 issued Aug. 7, 1973 Allen 3,733,794 issued May 22, 1973 Peterson 3,736,729 issued June 5, 1973 Harkness 3,782,084 issued Jan. 1, 1974 Braun 4,002,190 issued Jan. 18, 1977 ______________________________________
The interlocking switch arrangements disclosed in the patents mentioned above operate to short the magneto coil or ground the electrical system of a magneto powered engine ignition system to prevent engine operation when various lawn mower components associated with the interlocking switches, for example, grass bags or grass discharge covers, are not in their proper operating positions. Such prior art interlocking switch arrangements, which require shorting of the electrical system to stop engine operation, are subject to failure if a wire breaks or an electrical connection opens because the circuit can not be completed to provide the short circuit required to stop engine operation.